The present invention relates to an electrode for a battery, particularly a nickel electrode for an alkaline storage battery and to a method of fabricating the same.
Electrodes for a battery are roughly classified into three types: paste-type, sintered-type and pocket-type. Recently, a method for fabricating paste-type electrodes has been widely used practically as a new method for fabricating nickel electrodes for alkaline storage batteries. The method comprises a step of filling a pasty mixture (hereinafter referred to as "paste") composed essentially of an active material powder into spaces formed in a substrate such as foamed metal or nonwoven fabric of nickel fibers having three-dimensional communicating spaces.
Such metal substrates have a high porosity such that the three-dimensional communicating spaces occupy 95% of the total substrate, and a maximal diameter of several hundreds .mu.m for each space. This facilitates filling of an active material powder or a paste directly into the spaces, and finishing the resultant metal substrates to electrodes in a simple process.
Conventional practical and specific methods of filling a paste of an active material into the spaces of a metal substrate include a method of vibrating the paste to squeeze it into the spaces, a method of rubbing and filling the paste into the spaces using a tool such as doctor's blade, a method of bringing the paste into contact with one face of a metal substrate while decompressing the other face so as to squeeze the paste into the spaces, and a method of spraying the paste onto the spaces of a metal substrate from a nozzle.
Of these, the rubbing method and the spraying method are superior from the point of uniform filling of the active material paste into the spaces of the metal substrate. If compared, the spraying method is superior to the rubbing method because the former is excellent in durability and is more easy and simple in manipulating and maintaining the device for filling the paste.
Despite the above-mentioned merits, the spraying method has a drawback that uniform filling of the paste into the spaces of a metal substrate, such as foamed porous metal substrate, is difficult. In other words, the spraying method comprises a step of spraying a paste onto both faces of a foamed porous metal substrate at a certain rate while discharging the paste from a nozzle and filling it into the spaces of the substrate. This is disadvantageous in that some portions of the paste which first enter the substrate and are arrested proximal to the surfaces of the substrate are sometimes removed by an impinging action of the remaining portions of the paste which are to be sprayed subsequently. It is also disadvantageous in that the paste which has impinged on the surface of the substrate is sprung back from the surface.
Therefore, the spraying method is unsatisfactory from the point of uniform filling of a preadjusted amount of a paste into the spaces of a porous metal substrate and is to be improved in various points in the future. From the practical point of view, further control of the variations (dispersion) in the filled amount of paste and battery capacity is strongly desired.